The wear life of a window sash is unnecessarily limited because of water damage. How this arises, is that during the winter months in the northern climate, when warm interior air comes into contact with a cold window, there is water condensation, and the condensed water forms on the existing barriers whether they be plastic or metal cladding, and gains access to the underlying wooden frame surrounding the window opening, there causing damage to the wood. In a brief time, the frame rots and the window or door either falls out of place or the frame must be replaced.
The state of the present art is such that these window constructions are inferior because they serve as inadequate thermal barriers, and are thus sources of heat loss from a heated or cold interior to ambient exterior temperature.
There have been numerous proposals to correct these deficiencies, including cladding the frame both from the inside and the outside with a metal or plastic sheeting. Other proposals are to give protective coatings, including varnishes, chemical penetrants and other such coatings. While helping to some degree, the wood frame, after exposure over a period of time, is penetrated by moisture, and rots or warps, and must then be replaced.
The described construction lacks sufficient insulation and thus the window becomes a serious source of heat loss in modern dwellings and office buildings.